1. Field of the Invention
The present invention generally relates to an apparatus for inspecting fiber-optic connectors. In particular, the present invention relates to a fitting tip of the hand-held fiber-optic inspection probe for properly aligning and imaging angled fiber-optic connector endfaces. The present invention further relates to inspection probes fitted with such a fitting tip.
2. Description of the Related Art
The widespread implementation of fiber-optic communications has created an urgent need for regularly inspecting and maintaining the large number of fiber-optic connectors, which are often situated behind backplanes or in locations which are very difficult to access.
It is well known in the fiber-optic communications industry that the endfaces of optical fibers within communication systems must be kept clean and undamaged, otherwise serious signal loss could result. The demand for cleanliness for fiber-optic endfaces has become even more stringent as the communication bandwidths increase and new communication technologies requiring higher laser power are applied.
Many types of inspection devices with microscopes are already available for inspecting endfaces of a fiber-optic connector to make sure the endfaces are undamaged and clean. When an inspection probe is used to view or image the endface of a fiber-optic connector embedded in a connector adapter, a fitting tip for the inspection probe is typically needed to provide a mechanical interface with the connector adapter. There are currently available on the market a large number of fiber-optic connectors and their corresponding connector adapters. Consequently, a large number of fitting tips are needed for different types of inspection probes and connector adapters.
Generally, the endface of a connector comes in two kinds of shapes or finishes: PC (physical contact) and APC (angled physical contact). The APC endface is inclined at a standard angle of 8°.
In order to clearly view or image a connector endface using an inspection probe, it is important to align the optical axis of the microscope optical system of the inspection probe so that it is perpendicular to the connector endface. In general, the alignment is facilitated by using a fitting tip to properly connect and align the inspection probe with the connector adapter at a certain angle.
For a PC connector, the fitting tip is only required to align the optical axis of the inspection probe align with the axis of the ferrule of the connector. However, for an APC connector, the fitting tip must also deflect the optical axis of the inspection probe by an angle of 8° relative to the axis of the connector ferrule. The deflection of the optical axis of the inspection probe can normally be achieved by the mechanical structure of the fitting tip.
Besides properly aligning the optical axis of the inspection probe with the connector endface, the fitting tip may also serve to ensure that the connector endface is positioned within the focusing adjustment range of the microscope objective of the inspection probe. This is because the focusing adjustment range of the microscope objective is usually very limited, e.g. just a few millimeters, and the connector endface is often relatively deep inside the connector adapter. The length of the fitting tip may be adapted to make sure that the connector endface is within the focusing adjustment range of the microscope objective of the inspection probe.
FIG. 1 and FIG. 2 illustrate the inspection of a fiber-optic connector 40 (which is an SC/APC Connector with an endface inclined at 8°) by an inspection probe 10 fitted with a fitting tip 20 designed specifically for the SC/APC Connector. FIG. 1 shows the connector 40, the connector adapter 30, the fitting tip 20 and the inspection probe 10 separately before they are connected for an inspection job. As shown in the exploded view in FIG. 1 and the broken-out section view in FIG. 2, when the endface 411 of the connector 40 is to be inspected, the connector 40 is inserted into one end 340 of the connector adapter 30 and the front end tube 231 of the fitting tip 20 is inserted into the other end 320 of the connector adapter 30; the back end tube 212 of the fitting tip 20 is mounted on the front portion 120 of the inspection probe 10 and fixed thereto by matching the male thread on the back end tube 212 and the female threaded knob 122 with female thread on the front portion 120 of the inspection probe 10.
In this arrangement, because the connector endface 411 is inclined at 8°, the normal 400 to the connector endface 411 at the center thereof and the axis 401 of the connector ferrule 410 intersect at the center of the connector endface 411 and form an angle of 8°. When inspecting the connector endface 411, the optical axis 101 of the microscope optical system of the inspection probe should be aligned with the normal 400 to the connector endface 411 so that the connector endface 411 is perpendicular to the optical axis 101 to achieve the best image. To ensure the alignment of the optical axis 101 and the normal 400, the fitting tip 20 is constructed such that, when it is connected to the connector adapter 30 and the inspection probe 10, the axis 204 of the front end tube 231 is aligned with the axis 401 of the connector ferrule 410, and the axis 201 of the back end tube 212 is aligned with the optical axis 101 of the inspection probe 10. As a result, the angle between the axis 204 of the front end tube 231 and the axis 201 of the back end tube 212 will be essentially equal to the inclined angle of the connector endface 411, namely 8° in this case.
As shown in FIG. 2, the fitting tip 20 has a light passing channel 205, and the connector adapter 30 has a light passing channel 305. The optical axis 101 of the microscope optical system is arranged to perpendicularly align with the connector endface 411 of the connector 40 and intersect with the axis 401 of the connector ferrule 410. In this application, because the transverse space inside the connector adapter 30 is broad enough to accommodate a fairly broad channel 205 of the fitting tip 20, the light from the connector endface 411 will not be unduly obstructed between the connector endface 411 and the first surface 1301 of the microscope objective 130 of the inspection probe 10. Consequently, as long as the working distance of the microscope objective 130 is long enough, the microscope optical system of the inspection probe 10 can be directly focused on the connector endface 411 for inspection to obtain a clear image.
This type of fitting tip as illustrated in FIG. 1 and FIG. 2 can be applied to many types of connectors, such as SC, FC Connectors with a standard 8° inclined endface.
However, for some types of connector adapters with a relatively deeper channel, the distance between the endface 411 and the first surface 1301 of the microscope objective 130 of the inspection probe 10 will exceed the working distance of the microscope objective 130, and therefore the microscope optical system of the inspection probe 10 cannot be directly focused on the connector endface 411. For such connectors, a relay lens can be disposed inside the fitting tip. The function of the relay lens is to form an intermediate image of the connector endface within the working distance of the microscope objective 130 so that the inspection probe 10 may focus on the intermediate image to obtain a clear image. Thus, the relay lens effectively extends the working distance of the microscope objective and allows the fitting tip to be lengthened to reach the connectors hidden deep inside the connector backplane, where the inspection probe is unable to reach.
As an example, FIG. 3A and FIG. 3B illustrate the application of a fitting tip 60 with a relay lens (or relay lens system) 630 to connector endface inspection, in which the connector adapter 50 is an OptiTap® Adapter. FIG. 3A shows the position of the fitting tip 60 relative to the inspection probe 10, the connector adapter 50 and the connector 40. When they are connected to inspect the connector 40 inserted into one end 530 of the connector adapter 50, the back end of the fitting tip 60 is mounted to the front portion of the inspection probe 10 and the front end of the fitting tip 60 is inserted into the other end 520 of the connector adapter 50.
The fitting tip 60 has a fitting tube 610 to fit inside the end 520 of the connector adapter 50 and a supporting tube 620 for mounting the relay lens 630. The inside surface 513 of the connector adapter 50 fits closely with the outside surface 613 of the fitting tip 60 so that the fitting tip 60 is stably fixed to the connector adapter 50. The fitting tip 60 further has a mechanical hole 612 inside the fitting tube 610 for mounting the supporting tube 620 in the fitting tube 610. The outside surface 622 of the supporting tube 620 fits closely inside the mechanical hole 612. The optical axis 101 of the microscope optical system of the inspection probe 10, the inclined connector endface 411, and the axis 401 of the connector ferrule 410 are also shown in FIG. 3B.
FIG. 4 shows the imaging geometry of the fitting tip 60 with the relay lens (or relay lens system) 630 shown in FIG. 3A&B. In this application, the fitting tip 60 (and therefore the relay lens 630) is positioned such that the optical axis 601 of the relay lens 630 is perpendicular to the connector endface 411 at the center therefore. Because the connector endface 411 has an inclined angle of 8°, the angle between the optical axis 601 of the relay lens 630 and the axis 401 of the connector ferrule 410 is also 8°.
FIG. 4 also shows that the optical axis 101 of the microscope optical system of the inspection probe 10 is aligned with the optical axis 601 of the relay lens 630. The image plane 631 of the relay lens 630 corresponds to the object plane 131 of the microscope objective 130 (at a point within the fitting tip 60). That is, the microscope objective 130 is focused on the image of the connector endface 411 on the image plane 631.
As shown in FIG. 4, two representative rays 602 and 603 in object space emitting from the center of the connector endface 411 enter the relay lens 630 and exit from the relay lens 630 as conjugate rays 602′ and 603′ in the image space, respectively. The image rays 602′ and 603′ converge on a point on the image plane 631 of the relay lens 630. As a result, the distance extended due to the relay lens 630 is:L=l+l′+dl wherein l is the distance between the connector endface 411 and the front surface 6301 of the relay lens 630, l′ is the distance between the back surface 6302 of the relay lens 630 and the image plane 631, and dl is the distance between the front surface 6301 and the back surface 6302 of the relay lens 630. When the magnification of the relay lens 630 is −1×, l is equal to l′ and the converging angle u′ of the image ray 602′ relative to the optical axis 601 of the relay lens 630 is equal to the emitting angle u of the ray 602.
However, the optics arrangement shown in FIG. 4 cannot be exactly applied to many other types of connectors, for example, E2000/APC, LC/APC, MU/APC, etc. This is because the connector adapters for these connectors have a relatively lengthy and narrow channel. As explained next, under this situation the fitting tip will encounter problems if the optical axis 601 of the relay lens 630 is kept perpendicular to the connector endface 411. As an example, FIG. 5A and FIG. 5B illustrate the application of a fitting tip with above relay lens arrangement to the E2000/APC Connector 70 (with an endface inclined at 8°) and the E2000 Connector Adapter 80. FIG. 5A shows that if the optical axis 601 of the relay lens system 630 of the fitting tip is arranged to be perpendicular to the connector endface 711 of the connector 70 and aligned with the optical axis 101 of the microscope optical system of the inspection probe, namely, if the angle α between the axis 701 of the connector ferrule 710 and the optical axis 601 of the relay lens system 630 is kept at 8°, the relay lens 630 will come in close contact with the inner wall 813 of the connector adapter 80. Otherwise, the diameter of the relay lens 630 will be fairly limited due to the space restriction, resulting in a limited optical aperture and thus a limited image resolution. It can also be seen that, with α=8°, the optical axis 101 of the microscope optical system is already very close to the edge 814 of the inner wall 813 of the connector adapter 80. So in essence half of the light emitting from the connector endface 711 will be blocked by the inner wall 813 of the connector adapter 80. As a result, the image viewed by the inspection probe will not be uniform in brightness and about half of the endface image will be dimmer than the other half.
In order to reduce the blocked amount of the light from the connector endface 711, a compromise solution is to reduce the angle α between the axis 701 of the connector ferrule 710 and the optical axis 601 of the relay lens system 630 (which is to be aligned with the optical axis 101 of the microscope optical system), as shown in FIG. 5B, α<8°. As a result, the optical axis 601 of the relay lens system 630 (and the optical axis 101 of the microscope optical system) will not be perpendicular to the connector endface 711 anymore, and thus the endface image as viewed by the microscope optical system will not be uniform in brightness and not synchronic in optimal focusing.